Brake actuators are conventionally used on heavy vehicles having pneumatic braking systems, including trucks, buses and tractor trailers. Conventional brake actuators include a cup-shaped flexible diaphragm, which is supported in the housing, and a piston having a piston plate which is spring biased against the diaphragm. Upon actuation of the pneumatic braking system, air pressure drives the flexible diaphragm and the piston rod or push rod of the piston to actuate the braking system of the vehicle. Conventional brake actuators generally also include an emergency chamber, which may be mounted on the service chamber, having a power spring, which actuates the piston of the service chamber when the pneumatic pressure of the vehicle braking system fails or when the vehicle is turned off, providing an emergency braking system for the vehicle and a parking brake.
The piston of a brake actuator includes a piston rod or push rod, which is generally welded to the piston plate. The welding of the piston rod to the piston plate, however, creates several problems. First, the heat of welding removes any protective coating which may be applied to the parts, requiring a rust protecting paint to the weld area. Rust may still occur, particularly at the weld area, reducing the strength and durability of the assembly. Second, the butt weld of the piston rod to the piston plate may fail, particularly under the bending load and the extreme conditions encountered with brake actuators for heavy vehicles of the type which utilize brake actors. As will be understood by those skilled in this art, brake actuators are mounted under the carriage of the vehicle or tractor adjacent the axles, wherein the brake actuator is subject to extreme temperature variations and road debris including water, salt and ice.
A primary object of the brake actuator piston assembly of this invention is to improve the integrity of the joint between the piston plate and piston rod. A further object is to reduce cost by eliminating the welding of the piston rod to the piston plate, the subsequent coating or painting of the welded joint and permitting the use of a protective finish, such as zinc dichromate finishes. Another object would be to reduce the weight of the piston assembly which requires a piston plate having sufficient thickness to prevent burn-through when the piston rod is butt welded to the piston plate.